North Korea has significantly expanded a key long-range missile base within the country, CNN reported Wednesday, citing new satellite images it obtained.

The satellite images apparently show that the Yeongjeo-dong missile base and a nearby site remain active and the North Koreans have continued to update them.

U.S. intelligence agencies and analysts have long known about the base at Yeongjeo-dong, but the images reveal construction on a new facility seven miles away, a site that has not previously been made public, CNN reported.

"Satellite images show that the base remains active. Moreover, in the past year North Korea has significantly expanded a nearby facility that appears to be another missile base," according to a report from the Middlebury Institute of International Studies at Monterey reported by the outlet.

The images also indicate that, as of August, North Korea continues to build a large underground facility that was started last year.

President Trump and North Korean leader Kim Jong Un agreed to a framework for denuclearization in June during their historic summit in Singapore, a deal which also included unspecified American security assurances.

But Jeffrey Lewis of the Middlebury Institute told CNN that "Construction on the previously unidentified site has continued even after the Singapore Summit" between Kim and Trump.

Lewis also told the outlet that the site's location makes it a candidate to launch North Korea's newest long-range missiles.

Administration officials, meanwhile, would not comment on when they became aware of the new site.

"We watch North Korea very closely. We continue to support the diplomatic process. We will not discuss matters of intelligence," Pentagon spokesman Lt. Col. Chris Logan told CNN.

Work on the missile site does not appear to violate any agreement the North has made with the United States, but some Trump administration officials are declaring that the isolated nation has not met its end of the deal made in Singapore.

National security adviser John Bolton said Tuesday that Trump believes he should hold a second summit with Kim because the North Korean leader hasn't lived up to commitments he made during their first meeting.